How do I read P(>limit)?
P(>limit) is the share of ensemble forecast members that reach your limit at the chosen hour. This guide shows where it appears, what the 40% mark and EXCEED tag mean, and why it is a member count rather than a calibrated chance.
ON THIS PAGE
Steps
Set your limit
Use the Limit stepper in the top bar, or the copy of it inside the inspector on a phone, and type the number from your own document. With no limit set, the hero readout says "P(>limit) · set your limit" and no odds are computed. The value you type is in the display unit you have chosen.
Set your working height
Use the Height stepper next to it. Height decides which ensemble level is read. At exactly 10 m the ensemble is for gust. At any other height it is for mean speed at the nearest level the ensemble offers, so a crane at 80 m is judged on speed, not gust.
Read the hero line
In the hero readout, the right-hand side of the detail row shows "P(>" followed by your limit and a percentage, for example "P(>25) 32%". When that figure is 40% or more, the word EXCEED appears beside it. It describes the hour you have selected on the time strip.
Scrub the time strip
Drag the strip or use the arrow keys. Cells turn ember where the P for that hour is 40% or higher. On desktop the legend at the right reads "P ≥ 40%". Ember cells appear only once the ensemble has loaded for your current limit, so give it a moment after changing the limit.
Check the member count
Look at the model chips and the ensemble note. A full pool reads like "n/n members" with the same number on both sides. If members are missing the label becomes "ENSEMBLE INCOMPLETE" with received over expected, for example 28/31, and you should treat the figure with more caution.
Tip: The exceedance fan beside the hero shows the same odds hour by hour.
01What the percentage counts
The ensemble is a set of forecast runs started from slightly different conditions. P(>limit) is the number of those members whose value at the selected hour reaches your limit, divided by the number of members. If 20 of 80 members reach it, you see 25%. It is a count of how many forecasts cross your line. It is not a statement that there is a 25% chance of an event, and the page labels it as uncalibrated member fractions for that reason.
02Which ensembles feed it
Three ensembles are pooled: GEFS from the United States, ECMWF ENS from the European centre, and ICON-EPS from the German weather service. Each contributes its members, and the control run counts as a member. Pooling gives a broader spread than any single model. The chips under the inspector list them as "label received/expected" with the height used, and a chip turns to the split style when members are missing.
03Which height and metric it uses
The ensemble is only available at 10, 80, 100 and 120 m for speed, and at 10 m for gust. For gust (used only when your height is exactly 10 m) the 10 m ensemble is used. For other heights below 45 m the 10 m speed ensemble is used. From 45 m upwards the instrument tries the two nearest of 80, 100 and 120 m, then falls back to 10 m. When the level differs from your height, a note says so, such as "Ensemble at 80 m, the nearest level the ensemble names (asset 70 m)".
04The 40% mark
The ember colour on the time strip and the EXCEED tag both use a fixed 40% threshold. It is built into the instrument and cannot be changed. It is a prompt to look at that hour more closely, not a stop signal. The lamp is a separate calculation: it can add a watch or stop when 20% or 60% of members are outside the envelope, and it also checks the plain forecast against your limit.
05Incomplete and missing ensembles
"ENSEMBLE INCOMPLETE 28/31" means fewer members arrived than the models should have supplied. The odds are still shown, but on a thinner pool. If an hour has fewer than 10 members in total, the odds for that hour are withheld altogether. If no ensemble loads, the hero shows a dash in place of the percentage, with a reason, and the ensemble chip carries no member count. A missing figure is never shown as zero, because zero would read as calm.
06When it will not match what you expect
The odds are computed for the limit you set a moment ago. Changing the limit or height restarts the request after a short pause of about half a second, and until it finishes the hero shows a dash. The odds can also differ from the lamp, because the lamp blends the plain forecast and the ensemble. And in Golf mode the "P(cross>limit)" per hole is an approximation built from 10 m speed percentiles, so it will not equal the hero figure.
Questions
What does P(>limit) mean?
It is the percentage of ensemble members that reach your limit at the selected hour. It tells you how many of the pooled forecasts cross your line, which is a good guide to how uncertain the hour is. It does not tell you what the wind will do.
Is it a real probability?
No. It is a raw fraction of members, with no calibration against past outcomes, and the page says so. Ensembles are often too narrow, so a low figure does not rule an exceedance out. Use it as one input beside the primary forecast, the observation and your own judgement.
Why is there a dash instead of a percentage?
Either you have not set a limit, the ensemble is still loading for your latest limit and height, the ensemble could not be fetched, or fewer than 10 members were available for that hour. The line next to the dash gives the reason. It never means zero.
Why does the P change when I change the height?
Because the height decides which ensemble level is read, and whether gust or speed is counted. At exactly 10 m it is gust. Elsewhere it is mean speed, which is usually lower than gust, so the odds against the same limit usually fall when you leave 10 m.
Can I change the 40% mark?
No. It is fixed in the instrument for the time strip, the EXCEED tag and the next-exceed row. Fleet lamps use their own fixed 40% and 70% thresholds.